The present invention relates to a process for repairing circuit connections.
As electronic parts have become smaller and thinner, the circuits formed therein have achieved higher density and are finer. In connecting these fine circuits, the use of conventional connecting material such as solder, rubber connector or the like is inappropriate, so that in recent years, an adhesive or a film (each being hereinafter referred to as a connecting member) exhibiting anisotropic electric conductivity has come to be used widely. In connecting fine circuits with this connecting member, a connecting member layer consisting of an adhesive containing a given proportion of an electric conductive material is provided between two circuit groups opposed to each other; pressure or pressure and heat is or are applied to establish electrical connection between each two opposing circuits of the two circuit groups and simultaneously to impart electrical insulation between adjacent circuits; thus, the two circuit groups opposed to each other are adhered and fixed.
As the film-shaped material having anisotropic electric conductivity only in the thickness direction according to the prior art, there is a sheet-shaped structure having electric conductivity in the thickness direction via electric conductive particles, obtained by dispersing electric conductive particles in a non-conductive resin so that the particles make no contact with each other and then shaping the dispersion into a sheet having substantially the same thickness as the diameter of the electric conductive particles, as disclosed in, for example, Japanese Patent Kokai No. 51-21192. Also, there is an attempt of connecting two opposing circuit groups by adhering and fixing the groups in contact with each other by the use of an insulating adhesive containing no conductive particles (e.g. Japanese Patent Examined Publication No. 46-43732).
In connection by these connecting members, when electrical connection is poor or when electronic parts or circuits become faulty after the connection, there is employed a process comprising tearing up each two connected circuits, removing the connecting member remaining on the circuits with a solvent or the like, and reconnecting the cleaned circuits with a fresh connecting member of the same type.
Also, in adhering a housing or other parts to an electronic part having unconnected circuits, with an adhesive, when the adhesive has been mistakenly adhered to the unconnected circuits and consequently the later connection is inadvertent, there is employed a process comprising wiping off the adhesive adhering to the unconnected circuits, with a cloth or a swab both impregnated with a solvent or the like.
In the above-mentioned processes for removing the adhesive, however, the partial removal of the adhesive is extremely difficult. For example, a connecting member of anisotropic electric conductivity is also used in connecting a number of electronic parts to a large-sized electronic part having a number of circuits; when part of the electronic parts connected to the large-sized electronic part is repaired, there are problems in that the above removal of the adhesive adversely affects the other connecting member(s), resulting in incurring poor connection and reduced reliability. For example, in connection of electronic parts generally used in a liquid crystal display material, as shown in FIG. 1(a), wherein ITO circuits on a glass substrate 1 are connected with a number of FPC substrates 2 by the use of a connecting member of anisotropic electric conductivity, there are used very fine circuits of, for example, 100 .mu.m, in width for each conductor (circuit) and 100 .mu.m, in distance, between two adjacent conductors; further, the distance between the two adjacent FPC circuits is as small as several hundreds of microns in some cases as a result of recent trend of lighter weight, smaller thickness and smaller size in electronic parts. In order to remove one of the FPC substrates 2 shown in FIG. 1(a) and effect reconnecting, that FPC circuit is peeled and the connecting member remaining on the glass substrate is removed by the above-mentioned conventional method of, after decomposition or dissolution, wiping off with a swab impregnated with a peeling solution, infiltration of the peeling solution to the adjacent FPC circuits is unavoidable, that is, even the connecting members of the adjacent FPC circuits are decomposed or dissolved and there are possibilities of an increase in connection resistance and reduction in reliability of connection.
In the above-mentioned conventional methods for removal of adhesive or connecting member, it is possible to use, in combination, a method of using an adhesive masking tape or the like to protect the portion not to be removed, from the peeling solution. In this case, however, the adhesive in the masking tape is decomposed or dissolved by the peeling solution, resulting in an unavoidable increase in connection resistance and a reduction in the reliability of connection.